In the context of next generation wireless networks, with a targeted commercialization time around year 2020, millimetre wave radio is considered for establishing two types of backhaul nodes, aggregation and non-aggregation backhaul nodes. Millimetre wave is the radio wave with wavelengths between approximately 1 mm and 10 mm, corresponding to frequencies from about 30 GHz to 300 GHz. Due to the large available spectrum bands, millimetre wave is preferable for carrying high bit rate data on the backhaul link. However, spectrum bands other than bands between 30 GHz and 300 GHz can also be used for the backhaul link.
One way to boost the channel capacity of the millimeter wave based backhaul link is to use Multiple-Input-Multiple-Output (MIMO) configurations, and very often LoS MIMO, for the transmitter and receiver of the backhaul link. Typical LoS MIMO systems use Uniform Linear Arrays (ULAs) for the transmitter and receiver.
In a typical ULA system, the transmitter and the receiver antenna comprise multiple antenna sub-arrays. One exemplary ULA system might include four antenna sub-arrays, where each sub-array has sixteen antenna elements. The antenna sub-arrays use multiple antenna elements to form narrow beams.
It is generally understood that the LoS MIMO channel capacity is at a maximum when the condition defined by the equation
            D      t        ⁢          D      r        =            λ      ⁢                          ⁢      R              V      ⁢                          ⁢      cos      ⁢                          ⁢              θ        t            ⁢              θ        r            is satisfied, where λ is the carrier wavelength; V=max(M,N) and M,N are the number of sub-arrays at the transmitter and receiver, respectively. The parameter R is used herein to denote the range or distance between the transmitter and the receiver. A distance between different antenna sub-arrays, the inter-distance between antenna sub-arrays, is denoted as Dt and Dr, respectively for the transmitter and receiver. The down tilting angles are denoted as θt and θr, for the transmit antenna and receive antenna, respectively. The link capacity is related to the down tilting angles θt and θr. Azimuth angle has negligible impact on the channel capacity for this case.
The above channel capacity maximization condition is applicable for three-dimensional (i.e. realistic) antenna deployment as well as two-dimensional deployment. Additionally, transmitter antenna configuration parameters, including inter-distance between antenna sub-arrays and down tilting angle, have the same effect on the channel capacity as receiver antenna configuration parameters. Similar methods of controlling transmitter antenna configuration parameters can be applied to control receiver antenna configuration parameters to achieve equivalent channel capacity.
The problem with the ULA system is that the antenna sub-array configuration, i.e. the antenna sub-arrays inter-distances Dt and Dr and down tilt angles θt and θr, is fixed and cannot be changed during the operation of the network. Thus, it can be difficult to achieve maximum or optimal channel capacity under certain conditions.
Accordingly, it would be desirable to provide a system for modifying the antenna sub-array configuration at a network node that addresses at least some of the problems identified above.